Thursday, November 24, 2011

http://www.jstor.org/pss/4085810According to this reference, for a long time, folks thought that birds evolved from "pseudosuchian archosaurs". Then that fell from favour and was replaced by a purported "direct derivation of birds from theropod dinosaurs".

When that was shown to be untenable, some folks moved to the idea that birds evolved from crocodile type ancestors. (Yes, crocodiles). But then that idea fell from favour and the folks moved to some purported vague dinosaur ancestry. But they do not give any specifics so that it can never be evaluated. Perhaps someone could do us all a favour and tell us what the current thinking is about the purported dino to bird lineage.

The presence of an external mandibular fenestra, along with morphological evidence elsewhere in the body of pterosaurs (serrated teeth, antorbital fossa present, fourth trochanter on the femur present), supports a placement of Pterosauria within Archosauriformes and is consistent with a position within Archosauria.

In several pterosaurs the medial or first premaxillary tooth was procumbent[excessiveinclinationoftheincisorteethtowardthelips]. It angled forward as well as downward. In B St 1967 I 276 (No. 6 of Wellnhofer 1970), the tiniest pterosaur, the anterior premaxillary tooth was procumbent.

The teeth of deinonychosaurs were curved and serrated, but not blade-like except in some advanced species such as Dromaeosaurus albertensis. The serrations on the front edge of deinonychosaur teeth were very small and fine, while the back edge had serrations which were very large and hooked.[3]

The most primitive members have four pairs of teeth in the premaxillae, such as in Caudipteryx[9] and in Incisivosaurus they are enlarged and form bizarrely prominent bucktoothed [procumbent] incisors.

[Yi qi] Like other scansoriopterygids, the head was short and blunt-snouted, with a downturned lower jaw. Its few teeth were present only in the tips of the jaws, with the four upper front teeth per side being the largest and slightly forward-pointing, and the front lower teeth being angled even more strongly forward.[1]

Friday, November 11, 2011

http://bigcat.fhsu.edu/biology/cbennett/flotsam/Bennett-2008-forelimb-myology.pdf"...the large size, great length, and unconventional arrangement such that it swung backward in flight position enabled digit IV to spread and support the wing yet fold it out of the way when the animal was not flying.Such an arrangement of fingers with one swinging away from the others is unique among vertebrates."Let's consider this "uniqueness".Whenever an explanation requires a characteristic that is "unique among vertebrates" we have to question whether this explanation is correct. After all, if someone says to you - okay here is how it worked. It worked in a way that is found NOWHERE ELSE IN THE VERTEBRATE WORLD. Then you have to think that perhaps that explanation is not correct. So I think we can put such an explanation to the side.

In case people are having trouble visualizing what I am proposing, work with your own hand. Hold your hand out, palm down. Your index finger is the wing finger so it is very long. Bend your index finger toward your palm. Now imagine that you could continue bending it in that direction so that the index finger would point back toward the elbow. That is what I am suggesting. Now the question arises as to how that could be accomplished, given the length of the index finger.I can see how that could be accomplished but if anyone would like to offer up a suggestion please do.

Here is how it could work:Begin with the pterosaur on all fours (or standing) with the index finger bent (toward the palm and then toward the elbow). The unfolding of the index finger is a combined motion of lifting the arm, rotating the arm slightly backward (palm back) and unfolding the finger. Then at the top of the arm extension, rotating the arm back again.

What I am saying does not require a vault launch method but it would work with that method as well. See video:http://www.newscientist.com/article/dn19724-did-giant-pterosaurs-vault-aloft-like-vampire-bats.html

Here is a basic question about the current thinking - that the 4th finger is the wing finger and that it is turned 90 degrees. Is it turned 90 degrees TOWARD the THUMB or 90 degrees AWAY from the THUMB? I have not seen any reference that explicitly answers that question.
Can anyone provide a reference that gives the answer to that question?

Monday, November 7, 2011

"The pterosaur wing membrane is divided into three basic units. The first, called the propatagium ("first membrane"), was the forward-most part of the wing and attached between the wrist and shoulder, creating the "leading edge" during flight."

"Here is an image of a White Ibis in flight showing full breeding plumage, in this instance the bird is pushing it's wings down and the arm is stretched out. As you can see, we get a good view of where the bones are positioned in the wing, notice that they don't run along the front of the wing. The elbow is set back from the leading edge and the bend in the arm is hidden by the Propatagium, a fold of skin inside the front part of the wing which connects to the shoulder and the wrist."

"Modern birdssustain their flight with an efficient ventilation system that keeps air flowing to their muscles. But no one knew how pterosaurs, the first flying vertebrates, powered their wings. A new study in PLoS One concludes that ancient pterosaurs, flying reptiles that lived 220 million to 65 million years ago, did much the same, with a mobile rib cage and a system of air sacs distributed throughout the bones to help move air around.""The researchers also studied the air spaces in pterosaur bones and concluded that they were associated with air sacs, arranged in patterns similar to those seen in modern birds.The bigger the pterosaur, the more air sacs, just like in modern birds. The air spaces help oxygen circulate and probably also made bones light enough for flight."

Note as always there are dissenting opinions:

"But matching anatomy in pterosaurs to modern animals may be misleading, says Jaap Hillenius, a functional morphologist at the College of Charleston in South Carolina. Pterosaurs left no descendants and are only distantly related to birds. It's possible that the new study is correct, Hillenius says, but he's skeptical. For example, he thinks the model of rib-cage movement doesn't allow enough air for active flight, and that the sternum was not strong enough to support such movement. "Until we find a living pterosaur," there's no way to know for sure—"and that's not going to happen."".

John Ruben et al. (1997, 1999, 2003, 2004) disputed this and suggested that dinosaurs had a "tidal" respiratory system (in and out) powered by a crocodile-like hepatic piston mechanism – muscles attached mainly to the pubis pull the liver backwards, which makes the lungs expand to inhale; when these muscles relax, the lungs return to their previous size and shape, and the animal exhales. They also presented this as a reason for doubting that birds descended from dinosaurs.[5][6][7][8][9]Critics have claimed that, without avian air sacs, modest improvements in a few aspects of a modern reptile's circulatory and respiratory systems would enable the reptile to achieve 50% to 70% of the oxygen flow of a mammal of similar size,[10] and that lack of avian air sacs would not prevent the development of endothermy.[11]Very few formal rebuttals have been published in scientific journals of Ruben et al.’s claim that dinosaurs could not have had avian-style air sacs; but one points out that the Sinosauropteryx fossil on which they based much of their argument was severely flattened and therefore it was impossible to tell whether the liver was the right shape to act as part of a hepatic piston mechanism.[12] Some recent papers simply note without further comment that Ruben et al. argued against the presence of air sacs in dinosaurs.[13]

A 2009 study showed that pterosaurs had a lung-air sac system and a precisely controlled skeletal breathing pump, which supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The presence of a subcutaneous air sac system in at least some pterodactyloids would have further reduced the density of the living animal.[18]Like modern crocodilians, pterosaurs appeared to have had a hepatic piston, seeing as their shoulder-pectoral girdles were too inflexible to move the sternum as in birds, and they possessed strong gastralia.[45] Thus, their respiratory system had characteristics comparable to both modern archosaur clades.

Note

This site presents the idea that pterosaurs (rather than dinosaurs) developed into birds. This is not an "evolutionism" vs. "creationism" issue.An "evolutionist" can say that the pterosaur to bird developments are due to neo-Darwinian means (random mutation and natural selection).On the other hand, a "creationist" can say that those developments are the acts of a higher intelligence.This site does not take a position on the "evolutionism" vs. "creationism" question.

Philosophy

Like most people, I have philosophical ideas that go beyond the nuts and bolts of the scientific analysis of the origin and development of birds.There are larger questions that philosophers have grappled with since the most ancient times. If anyone is interested in my take on those more philosophical ideas, click here.But please realize that all the ideas of this site are pure materialist, scientific ideas supported by physical evidence and scientific studies.

The 19th-century German philosopher Arthur Schopenhauer astutely summarized the three stages through which all truth passes: first, it is ridiculed; second, it is violently opposed;

and third, it is accepted as being self-evident.

"In the choice between changing one's mind and proving there's no need to do so, most people get busy on the proof."~John Kenneth Galbraith

Keywords

origin of birds, pterosaur is the ancestor of modern birds, birds did not evolve from dinosaurs, cladistics, stratocladistics, Cretaceous, Mesozoic, fossil record, BAD, BAND, birds are not dinosaurs, flightless birds, aves